To Make Shortbread Base: Cut butter into 1/2-inch pieces. In a food processor process all ingredients until mixture begins to form small lumps. Sprinkle mixture into a 9 x 13 x 2-inch baking pan and with a metal spatula press evenly onto bottom. Bake shortbread in middle of oven until golden, about 20 minutes. While shortbread is baking, prepare topping.

*Note: Line baking pan with aluminum foil or parchment paper, so bars are easier to cut and remove from pan.

To Make Lemon Topping: Preheat oven to 350°F (180°C).

In a bowl whisk together eggs and granulated sugar until combined well and stir in lemon juice and flour. Pour lemon mixture over hot shortbread. Reduce oven temperature to 300°F (150°C) and bake in middle of oven until set, about 30 minutes. Cool completely in pan and cut into 24 bars or triangles. Sift confectioners' sugar over bars before serving.